This invention relates to a light-sensitive lithographic plate, specifically a light-sensitive lithographic plate which is improved in surface characteristics of a support, and more specifically a light-sensitive lithographic plate having an improved hydrophilic layer.
Light-sensitive lithographic printing plates, for example, positive light-sensitive printing plate, were conventionally composed of a support having a hydrophilic layer and a light-sensitive layer having ink affinity provided thereon. Lithographic printing plates are obtained by conducting an image exposure on a light-sensitive layer of such light-sensitive lithographic printing plates, developing the light-sensitive layer having been exposed by use of a developer to remove the exposed light-sensitive layer and have the surface of the hydrophilic support exposed, while the light-sensitive layer of the unexposed portion remains on the surface of the support to form image portions having ink affinity.
The printing using such lithographic printing plates is done by utilizing repellent or non-miscibility between water and oil. Specifically, after having the non-image portions of the printing plate wetted with water, applying an ink on the printing plate, then the ink is repelled by the wetting water or dampening solution on the non-image portions, resulting in selective deposition of ink only on the image portions. Transferring the ink on the image portions to the image-receiving material, printing matters having images corresponding to the above image portions are obtained.
Accordingly, the support for obtaining such a lithographic printing plate is required to have excellent hydrophilicity and water-retention when it is dipped in water, as well as good adhesion property with a light-sensitive layer which receives printing press. The light-sensitive layer is required to have ink affinity, high sensitivity to exposure, and also, as the most important condition, high press life.
As the support satisfying these conditions, most excellent is an aluminum plate. For obtaining enough adhesion property between the aluminum plate and the light-sensitive layer, there have been described, as a surface treating method for mechanically roughening the surface of the support, for example, Ball graining, Wire graining, Brash graining and other methods in Japanese Patent Publications No. 40047/1975 and No. 46003/1976, etc. Also, an electrolytic roughening method, by which a uniform and dense grain configuration is formed on the surface of the aluminum plate by using a hydrochloric acid bath, a nitric acid bath and the like and by applying direct or alternating current, is described in Japanese Patent Publication No. 28123/1973, U.S. Pat. No. 4,087,341, Japanese Unexamined Patent Publication No. 67507/1978, etc. Furthermore, Japanese Unexamined Patent Publication No. 150595/1981 discloses a method for controlling adhesion property between a support and a light-sensitive layer by effecting sealing treatment by use of hot water, sealing treatment by use of silicate, etc. onto the surface of the support.
As described above, further surface treatments are applied for imparting sufficient adhesion property between the support and the light-sensitive layer, as well as enhancing hydrophilicity and water retention of the support such as aluminum plate. For example, as such surface treatments, described in the specifications of Japanese Patent Publication No. 22063/1981, U.S. Pat. No. 2,246,683 and U.S. Pat. No. 3,160,506 were to enhance hydrophilicity and water retention of a metal surface by chemically treating the metal surface with use of potassium fluorozirconate to form a coating film. Also, Japanese Unexamined Patent Publication No. 131102/1978 describes a support whose hydrophilicity and water retention are enhanced by treating it with an aqueous solution of potassium fluorozirconate and subsequently an aqueous solution of sodium silicate.
However, in these methods, problems occur in press life and resistance to chemicals, when an effect of preventing stain in the non-image portions of lithographic printing plate obtained through development processing (hereinafter referred to as anti-stain effect) is sufficiently improved, while the effect becomes insufficient when the press life and resistance to chemicals are improved, accordingly it was difficult to improve three of anti-stain effect, press life and treating chemical resistance at the same time.
Such phenomenon appears more significantly when burning treatment is conducted which has been generally employed as a means for enhancing press life. The lithographic printing plate obtained from the support which was treated by the method mentioned above is no more applied to practical use.
The present inventors have extensively made researches in the light of the above problems, and found that a light-sensitive lithographic printing plate having high press life as well as enough water retention at the nonimage portions and being free from stain at the nonimage portions can be obtained by treating a surface of mainly aluminum support by use of specific treatment, resulting in accomplishment of this invention.